AFR Small-Block Heads - Calculatus Eliminatus

Testing AFR's New Eliminator Small-Block Cylinder Heads.

This is how AFR's Tony Mamo spends his rainy days, locked away with a grinder looking for hidden horsepower.

Paraphrasing Dr. Seuss's magnificent Cat-in-the-Hat, "Calculatus Eliminatus is the best friend that you've got; the way to find the missing horsepower is to find out where it's not!"

As we all know, the process was quite effective in locating one missing moss-covered, three-handled, family whatever it was, but the same principle holds true when you spend that rainy day searching not for family feline brick-a-brack, but for absentee airflow. Just ask AFR's own Tony Mamo, the cat inside the hat so to speak, as his monumental task was to take an already impressive AFR small-block cylinder head and make it even better.

Given their impressive performance, it's hard to believe that the original AFR line of small-block heads dates way back to 1991. Available in port volumes ranging from 180cc to 210cc for the street heads and all the way up to the 227cc for the race versions (AFR also makes a 215cc raised port race head), testing has proven the complete AFR lineup to offer impressive airflow (especially given the port volumes).

Better yet, AFR has made sure all of the airflow offered by its small-block heads converted directly to horsepower. Big flow numbers are one thing, but big flow numbers that produce equally big power numbers are what distinguish a good head from a great one.

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Since it was time to retool, AFR took this opportunity to refurbish the existing line of small-block Chevy heads. As is often the case, the simple refurbish turned into a whole new head. The new Eliminator series offers a weight savings of 4 pounds (compared to the original AFRs), improved oil drain back and a sizable increase in airflow.

Despite the impressive power production offered by the existing line, AFR decided it was high time to up the power ante. Not surprisingly, revamping the lineup coincided with retooling the product line. Rather than simply retool to streamline the production process, the gang at AFR decided to use the opportunity to upgrade its existing SBC product line. This is obviously good news for enthusiasts, as we have managed to produce exceptional power numbers with the previous AFR small-block heads and having an upgraded version will help take any build (mild or wild) to the next performance level.

Revamping the product line sounds easy while standing around water cooler, but actually putting into action takes a great deal of hard work. That is where Mamo comes in, as he was the man responsible for creating the new Eliminator line of AFR SBC heads. This was no easy task given the already impressive performance, but with porting tools, knowledge and experience, Tony set to work on redesigning the ports, chambers and even valve train to modernize the 23-degree heads.

Having had such good success with its big-block Chevy and new LS-series heads (for the LS1, LS2 and LS6), they decided the original small-block deserved equal attention.

In fact, many of the improvement ideas came from the LS-head program, namely the valvetrain upgrades. Tony went looking for two things when reviewing the existing valvetrain package, namely improving flow and reducing mass. The additional flow is somewhat self explanatory, but a reduction in valvetrain mass will improve the rpm potential of the motor, thus allowing more power at higher engine speeds. There is nothing more frustrating than having valve float ruin a perfectly good power curve. Things are going well, the power is climbing and all of a sudden the engine note roughens and the power heads due south. While the typical cure is to increase the valve spring rate, another approach is to decrease the weight of the components that make up the valvetrain (i.e. valves, springs, retainers and keepers).

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The new Eliminator heads were also treated to a valvetrain upgrade, including the use of smaller diameter (lighter) valve springs and retainers. Shown (from right to left) are the spring package used on the original AFRs, the standard and optional spring packages for the new Eliminator heads. The titanium retainers used on the optional springs offered a weight savings of 9 grams.

Valve control is a function of engine speed, spring rate and valvetrain mass. Valve control is proportional to spring rate and inversely proportional to engine speed and valvetrain mass, so a decrease in either will improve valve control. The downside to increased spring rate is an increase in friction losses and a possible reduction in power, thus maximizing control with the minimal spring rate is actually ideal. This is where a lightweight valvetrain comes into play, as not only does the improved valve control allow higher engine speeds, but it is possible to actually improve the power output by not resorting to excessive spring rates.

Tony went after every component on the valvetrain, including the valves, springs, and retainers. He even saved 3.5 grams (per pair) by upgrading the keepers. More than simply a weight savings exercise, Tony used the opportunity to actually improve keeper strength by replacing the standard square-cut keepers with bead-lock versions. The bead-lock keepers eliminate the point loading of the square cut keepers by spreading the retaining load over a greater surface area.Thus the new design is not only lighter, but also stronger.

The keepers were just the start, as Tony turned his attention to the spring package and valves. The spring package was upgraded with the new double springs from the LS1 heads. The smaller-diameter springs combined with a new retainer to drop the total package weight by a whopping 33 grams. While 33 grams may not sound like much on a 3500-pound car, the fact that this package must cycle as much as 100 times per second (or more) means an exaggerated relative mass.

Weight conscious individuals can further reduce valvetrain mass by 9 grams with the use of titanium retainers (used with the optional 8019 spring upgrade). The standard 8017 springs (135-punds of seat pressure and 320 pounds open) will accept up to .600 lift, but when nearing that maximum lift value, AFR recommends stepping up to the 8019 springs (155 pounds seat and 412 open), as the spring upgrade will also allow cams with up to .650 lift. Naturally AFR has a spring package for solid roller cams available for the new Eliminator heads.

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AFR Small-Block Heads - Calculatus Eliminatus

This is how AFR's Tony Mamo spends his rainy days, locked away with a grinder looking for hidden horsepower.

Since it was time to retool, AFR took this opportunity to refurbish the existing line of small-block Chevy heads. As is often the case, the simple refurbish turned into a whole new head. The new Eliminator series offers a weight savings of 4 pounds (compared to the original AFRs), improved oil drain back and a sizable increase in airflow.

The new Eliminator heads were also treated to a valvetrain upgrade, including the use of smaller diameter (lighter) valve springs and retainers. Shown (from right to left) are the spring package used on the original AFRs, the standard and optional spring packages for the new Eliminator heads. The titanium retainers used on the optional springs offered a weight savings of 9 grams.

The new Eliminator heads also received valve upgrades. The new valve not only offered undercut stems, but (more importantly) 8mm stems. Dropping down from the conventional 11/32nds stems to the smaller 8mm stems (stem size shared with the LS1 heads) on the intake valves knocked off another 15 grams.

AFR's Tony Mamo left no stone unturned in his search for additional airflow. The combustion chamber received a great deal of work, as it is a critical element in the quest for power. As with the previous AFR heads, the Eliminator heads will be made available in 64 and 76cc chambers.

Only after the original port was finished was the digitizer brought out to replicate the new port design.

The bowl area was also reshaped to improve the airflow without resorting to increased port volume.

On the 195 heads used for testing on the 383 stroker, the revised exhaust ports measured 75cc and flowed over 210 cfm.

The new Eliminator heads were developed the old fashion way, with a hand grinder on the flow bench.

While we see the springs, retainers and guide plates, if you look closely you'll see that the new AFR Eliminator heads featured improved oil drain back thanks to revisions in the original casting.

Tested on the 383 stroker from American Speed, the new Eliminator heads offered roughly 35 hp and 20 lbs-ft of torque over the already powerful original AFR 195s.

Read all about how to choose the propper spring rate for your suspension system and adjustment tips from Chassisworks. Only at www.chevyhiperformance.com, the official website for Chevy High Performance Magazine! » Read More